III-Nitride semiconductor devices are well known. In such devices, a 2-DEG conductive layer is formed at the boundary surface between two layers, for example, a bottom GaN layer and a top AlGaN layer. Spaced source and drain electrodes are connected to the AlGaN layer. A gate electrode, which may be an insulated gate or Schottky gate is disposed between the source and drain electrodes. When a gate potential is applied to the gate, the 2-DEG layer under the gate is interrupted. Thus, the device is normally conductive and “on” (in the absence of a gate signal) and is turned “off” in response to the gate signal. The device is therefore a normally on switch and is a depletion mode (D-mode) device.
In many applications it is desirable to have a normally off switch device which is turned on in response to a gate signal (an enhancement mode or E-mode device). The use for a depletion mode device is such applications complicates the drive circuitry and adds cost when it is desired to otherwise employ the desired characteristics of the III-Nitride device.
Structures are known to make a III-Nitride device operate as an enhancement mode device. These arrangements, however, require complicated processing steps and circuitry. It would be very desirable to form an enhancement mode III-Nitride device which employ standard processing technology.